1. Field of the Invention
The invention relates to a displaying method and an image display device, and more particularly, to a displaying method and image display device capable of improving the color shift phenomenon.
2. Description of the Prior Art
As incident lights passing through a liquid crystal layer from different angles generate different retardations, the refractive index of the light transmission will change according to different observation angles and result in different transmittance and different brightness while viewing from different angles. Hence, the light transmittance of a liquid crystal display being viewed from the front is different from the light transmittance of the same liquid crystal display being viewed from a side. Therefore, the brightness of the light will change according to the viewing angle. Additionally, a color shift phenomenon will result when different colors of light (such as red light, green light, and blue light) are combined at different brightness while viewing from the front and a side of the LCD. The degree of color shift among the three primary colors is as follows: blue light>green light>red light. Consequently, how to effectively improve this color shift phenomenon while viewing color displays from both front and sides has become an important task.
U.S. Pat. No. 5,717,474 to Kalluri, which is incorporated herein by reference, has suggested a display of dividing a pixel into a plurality of regions with different characteristics adapted for viewing from different angles. However, after the display is fabricated, no further adjustment can be made, and the fact that different regions correspond to different viewing angles specifically also reduces the quality of the display.
U.S. Pat. No. 5,847,688 to Sasumu, which is incorporated herein by reference, has suggested a method of utilizing different drivers to input the original signal within every two frames according to two gamma curves of different viewing angles. However, changes made within every two frames will result in flickering and only half of the pixels are actually involved in the displaying of an image at a particular viewing angle, thereby reducing the quality of the image and failing to solve the problems that occur in most observation circumstances.
U.S. Pat. No. 6,801,220 to Paul et al., which is incorporated herein by reference, has suggested a method of utilizing more than 2×2 subpixels to display an image, utilizing calculated values to adjust the original image, and utilizing bright and dark pixels of different ratios to complete a display. However, under the circumstances of utilizing a plurality of pixels to display various actions and treating each pixel as an individual unit, a resolution of greater than 170 dpi is required to solve problems such as color shift.
Please refer to FIG. 1. FIG. 1 is a diagram showing a conventional arrangement of the subpixels of a color display 10. As shown in FIG. 1, the conventional color display 10 (such as a liquid crystal display) includes a plurality of pixels 11 and 12 arranged in a matrix. Preferably, each of the pixels includes two red subpixels R, two green subpixels G, and two blue subpixels B, which are arranged in stripes. The pixel 11 includes a first red subpixel 111, a second red subpixel 112, a first green subpixel 113, a second green subpixel 114, a first blue subpixel 115, and a second blue subpixel 116.
Since the bright state signals and dark state signals have the low color shift characteristics, the conventional image display primarily divides a color subpixel into two smaller subpixels. The two smaller subpixels are driven by a bright state signal and a dark state signal and the combined gray scale is used for displaying the desired color, thereby improving the color shift under large viewing angles and expanding the overall viewing angles. As shown in FIG. 2, the first red subpixel 111 is driven by a bright state red signal, the second red subpixel 112 is driven by a dark state red signal. In FIG. 2, the cross hatching indicates the subpixels driven by dark state signals. The combined effect of the first red subpixel 111 and the second red subpixel 112 forms the desired red color of the first pixel 11 for improving the color shift and viewing angle of the red color of the first pixel 11. Similarly, the blue subpixels and the green subpixels are driven by the same method for improving the overall color shift problem and viewing angle of the first pixel 11.
The normalized light transmittance between a side-view and a front-view will differ even with color lights that have identical gray scales, thereby producing a color shift phenomenon. The difference of the normalized light transmittance between the side-view and the front-view decreases and reaches 0% as the gray scale reaches 0 or 255. Hence, for example, when the original gray scale of the blue pixel is 128, a dark state signal (hence, the dark state gray scale) can be selected as 0, and a bright state signal (hence, the bright state gray scale) can be selected as 190. The selected values, including both the bright state gray scale and the dark state gray scale, are utilized as a calibrated gray scale group to achieve the same visual effect as produced by the original gray scale. Since the difference of the normalized light transmittance between the side-view and the front-view of the calibrated gray scale group is significantly smaller than the difference of the normalized light transmittance between the side-view and the front-view of the original gray scale 128, the calibrated gray scale group can significantly reduce the color shift phenomenon on a liquid crystal display while maintaining an equivalent amount of brightness as the original gray scale.
The liquid crystal displays described involve the utilization of pixels, in which the subpixels driven by the bright state signals are concentrated in one row, whereas the subpixels driven by the dark state signals are concentrated in another row, as shown in FIG. 2. Consequently, stripes caused by uneven brightness will appear on the display image and result in unsatisfying visual effects. Additionally, the fact that the subpixels are not effectively arranged also reduces the sampling and rebuild ability of the image signals. Hence, the fabricated resolution must be doubled in order to achieve a resolution equivalent to the original fabricated resolution.
Therefore, how to develop an enhanced color display for solving the above-mentioned problems has become an important task.